Basic research in biological rhythms can be related to affective illness with respect to (1) the involvement of disturbed circadian rhythms (24 hour cycles) in the pathophysiology of the illness and (2) the inherent cyclicity of the illness (itself a type of biological rhythm). Previous clinical investigations of many physiological and biochemical variables have shown that circadian rhythm phases, amplitudes and waveforms are abnormal in some depressives. The apparent abnormalities in circadian rhythms seen in depressive disorders may arise from alterations in length of these rhythms (the free-running period), the interactions between rhythms, or in the effect which environmental cues (zeitgebers) have on these rhythms. The timing of circadian oscillators cannot be measured directly in humans and indirect measures such as the secretory profiles of hormones, body temperature and EEG recorded sleep must suffice instead. External and internal factors called masking can influence the apparent circadian rhythms in these variables without affecting the biological clock or clocks. Physical activity, diet environmental lighting, differing sleep schedules and stress are common forms of masking. Differences in circadian rhythms between normals and depressives would arise from differences in masking rather than in the intrinsic properties of the biological clocks. The present study is designed to compare the circadian rhythms of depressed patients and normal controls in conditions where the internal and external sources of masking have been controlled. Rhythms in cortisol, melatonin, TSH, neurotransmitter metabolites CHVA, MHPG, 5HIAA, core body temperature, sleep and activity will be assessed.